[Rayan]

Hi,
we had a lab today but i didn't really understant what were doing and why.. When i asked the Dr, he talked and talked and talked and didn't answer my question :s
we took a sample of white portland cement, to which we added ammonium chloride, and then hydrochloric acid. i understood that it's something about the fact that SiO2 is not soluble in the solution and precipitates, we filtrated the solution and then we had to weight the SiO2 to determine its percentage in our sample. did i get it right?? if yes, what are the reactions occuring? is there any websites that might help me?
thanks in advance

[ARGOS++]

Dear Rayan;

Yes! – You are doing right.

For SiO₂:
As first reaction the also first & second reactions under “Hardening” on: 

"Portland Cement”

     - takes place (Maybe the Ammonium chloride gives a better precipitation.)
The use of HCl speeds up the reaction and builds the soluble Calcium Chloride.
Therefore take a look under:  "Calcium Chloride”

Good Luck!
                    ARGOS⁺⁺